Yukio Agatsuma

Diterpenoid feeding-deterrents from Laurencia saitoi

Abstract Three new diterpenes and 14 known, brominated and non-brominated diterpenes have been isolated from the red alga Laurencia saitoi collected in ‘Isoyake areas’ in the Sea of Japan. Some of these diterpenes showed significant feeding-deterrent activity against young abalone ( Haliotis discus hannai ) and young sea urchins ( Strongylocentrotus nudus and S. intermedius ), thus suggesting that these metabolites provide a chemical defense against marine herbivorous animals in ‘Isoyake areas’.

The ecology of Tripneustes

This chapter discusses about the ecology of Tripneustes a circumtropical genus that extends into the subtropics. Tripneustes appears to be a generalist in habitat. Tripneustes has early maturation, rapid growth, high gonadal production, sporadic recruitment, and short longevity. All are characteristics of an mderal species. This chapter also highlights the three extant species of Tripneustes—that is, Tripneustes gratilla, Tripneustes ventricosus, and Tripneustes depressus. Tripneustes gratilla is one of the most common sea urchins of the intertidal and littoral zones of the coral reefs of the Bonin Islands. Tripneustes ventricosus is probably the first sea urchin whose fisheries were managed, with a closed season during the peak of the breeding season. A tabular representation of Tripneustes Habitat, density, and food habits is also highlighted in the chapter.

Ecology of Strongylocentrotus intermedius

This chapter gives an insight into the ecology of Strongylocentrotus intermedius commonly found on the rocky bottom in shallow waters around Hokkaido. It is harvested commercially in Iwate, Aomori, and Hokkaido, Japan. The roe is eaten mainly as sashimi, sushi, and served in a bowl with rice Salted raw urchin is a familiar food in Hokkaido. Strongylocentrotus intermedius is adapted to cold waters. As with other strongylocentrotids, it feeds mainly on kelp. The chapter also elaborates upon the other factors of Strongylocentrotus intermedius such ageographical distribution, reproduction, Spawning structure, larval ecology, distribution, settlement and metamorphosis, food habits, food and growth, water temperature, and habitat structure, bio-economy, and recruitment. A diagrammatic representation of the Spawning seasons of Strongylocentrotus intermedius in Hokkaido waters is also presented in the chapter.

DISTRIBUTION OF THE SEA URCHIN HEMICENTROTUS PULCHERRIMUS ALONG A SHALLOW BATHYMETRIC GRADIENT IN ONAGAWA BAY IN NORTHERN HONSHU, JAPAN

Abstract Distribution of the sea urchin Hemicentrotus pulcherrimus was monitored monthly or bimonthly from April 1998 to May 1999 at a 100 m2 permanent site in intertidal to subtidal zones at depths of up to 2.8 m in Onagawa Bay, northern Honshu, Japan. Factors causing seasonal demographic changes were analyzed from vertical algal vegetation, sea urchin size, gonad development, and gut content. The highest density of H. pulcherrimus was found on algal turf on boulders at the depth of 0–0.3 m. Migration of adult sea urchins on crustose corallines at the depth of 0.3–2.8 m to the algal turf and subsequent inhabitation in more suitable boulder habitat are suggested from November to March, when Acrosorium polyneurum, which is their main food, grew dominantly. As the high gut content of crustose coralline of the sea urchins on crustose corallines resulted in significantly lower gonad indices, it is likely that migration is caused by their high foraging activity for A. polyneurum to ensure gonad development. The growth of the sea urchins on algal turf was ensured by Chondrus spp. as main food.

Reproduction of sea urchin Loxechinus albus in Chiloé Island, Chile

During 1986–1989, the seasonal maturation and gonad index (gonad weight/body weight × 100) of adult Loxechinus albus were examined at nine sites, and the appearance of fourarmed echinopluteus larvae was investigated at three sites off the eastern coast of Chiloé Island, Chile. Spawning occurred during November–January when the gonad indices fell to a minimum, the number of mature specimens decreased and four-armed larvae appeared, corresponding to the rise in water temperature. The number of four-armed larvae appearing at the northern site was markedly less than that at the southern site. The sea urchins matured in January and February immediately after spawning at many sites and a high percentage of maturation lasted for a long period at some sites. These findings are considered to be associated with high food availability and annual narrow ranges of water temperature.

Chapter 28 – Strongylocentrotus intermedius

Strongylocentrotus intermedius is adapted to cold waters. As with other strongylocentrotids, it feeds mainly on kelp. Populations in the eastern Pacific Ocean and Sea of Okhotsk differ from those in the Sea of Japan. Current recruitment is high in the Sea of Okhotsk and is poor in the Sea of Japan and Pacific Ocean. Ecological and genetic studies should be done to investigate the differences between these populations for their conservation, sustainable fishery production, and aquaculture.

Ecology of Hemicentrotus pulcherrimus, Pseodocentrotus depressus , and Anthocidaris crassispina in southern Japan

This chapter elaborates about ecology of Hemicentrotus pulcherrimus, Pseudocentrotus depressus, and Anthocidaris crassispina which are important fishery resources and occur in the shallow waters of southern Japan. Hemicentrotus pulcherrimus have a bitter taste therefore are not eaten raw and are preserved in small bottles mixed in brine or alcohol. Among them only Anthocidaris crassispina seems to form extreme population densities that result in over-grazing. Hemicentrotus pulcherrimus has low mortality, short time to maturity and great effect of low food level on growth. This chapter also highlights in detail the characteristics of each in terms of their geographical distribution, reproduction cycle, larval ecology, food habits, growth, and population dynamics.

NORTHWARD EXTENSION OF GEOGRAPHIC RANGE OF THE SEA URCHIN HEMICENTROTUS PULCHERRIMUS IN HOKKAIDO, JAPAN

Abstract In the early 1990s, the geographic range of the sea urchin Hemicentrotus pulcherrimus from the Sea of Japan increased from off southwestern Hokkaido to off northern Hokkaido. This was caused by episodic recruitment in 1989, 1990, and 1991. These recruitments coincided with high water temperature during the larval periods (March to May). In 1993, H. pulcherrimus, at a density of 2.4 individuals/m2 derived from those three year classes, was found at a depth of 2–3 m in Tomari, where it had not been found in 1989. In Oshoro Bay, this sea urchin appeared dramatically in 1990, reached a peak density of 5.3 individuals/m2 in 1992, consisting mainly of 1989- and 1990-y classes. The high-density level of >2 individuals/m2 continued until 1998. Afterwards, no marked recruitment was found, corresponding to low water temperature in spring, and the density decreased markedly to 0.1 individuals/m2 in 2005. High water temperature in the 1990s is more likely to be responsible for the reproductive success of H. pulcherrimus extending to the north. This study suggests the colonization and persistence of the population in the northern district over the species range in 1990s were closely related to the highest seawater temperature in the 20th century.

Ecology of Strongylocentrotus nudus

This chapter gives an insight into the ecology of Strongylocentrotus nudus a dominant sea urchin species in the northwest Pacific. Strongylocentrotus nudus is harvested commercially in the Pacific Ocean from Ibaragi to Hidaka, Hokkaido, and in Sea of Japan from Toyama to Soya, Hokkaido. Strongylocentrotus nudus is the most commonly harvested edible sea urchin in Japan and accounts for about 44% of the total commercial harvest. Juveniles are produced artificially and transplanted off the Pacific coast of Tohoku to increase harvest. Its high growth rate, long longevity, high reproductive efforts, and reproduction after period of maximum feeding and growth responses to food availability are characteristics of a competitive species. The population biology of Strongylocentrotus nudus is not well known and studies on the effect of biotic and abiotic factors must be done. This chapter also covers the geographic distribution, reproductive cycle, larval ecology, metamorphosis and settlement, food selectivity, somatic growth, juvenile habitat, and population of Strongylocentrotus nudus.

Inhibitory effect of 2,4‐dibromophenol and 2,4,6‐tribromophenol on larval survival and metamorphosis of the sea urchin Strongylocentrotus nudus

As a possible factor leading to the low recruitment level of sea urchins in kelp forests, the inhibitory effect of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP) released from the large perennial brown algae Ecklonia kurome and Eisenia bicyclis on survival and metamorphosis of eight-armed larvae of the sea urchin Strongylocentrotus nudus was examined. The percentage of larvae that underwent metamorphosis in filtered sea water after 1 h exposure to one-half dilution of saturated dibromomethane solution (≈60 ppm) as a chemical inducer reached approximately 100% after 1 h, while that in filtered sea water containing 1 ppm TBP was reduced to 73%. This was further reduced to less than 40% in the presence of 10 and 20 ppm TBP after 2 h. In filtered sea water containing 1 and 10 ppm DBP, the proportion of metamorphosed larvae was reduced markedly to 43 and 5% after 2 h, respectively. All larvae exposed to 50 ppm TBP and to 20 and 50 ppm DBP died after 1 h. These findings suggest that DBP is more toxic than TBP for sea urchin larvae, strongly inhibiting their metamorphosis.